Human leukemia associated antigens are detected by nonhuman primate antisera to leukemic cells from donors with different morphological classes of leukemia. In addition antisera to RNA tumor viruses are studied for their reactivity with human leukemia cells. The antisera are tested by complement dependent cytotoxicity and the specificity of the antisera established by absorption techniques. The serologically defined simian antisera are then evaluted as diagnostic and nosology reagents and clinical management aids. In addition the antisera are used to monitor the antigens in studies designed to isolate them and identify their molecular characteristics. BIBLIOGRAPHIC REFERENCES: Metzgar, Richard S., Mohanakumar, T., and Bolognesi, Dani: Relationships between membrane antigens of human leukemic cells and oncogenic RNA virus structural components, J. Exper. Med. 143: 47-63, 1976. Mohanakumar, T., Metzgar, R. S. and Miller, D.S.: Antigenic markers for human leukemia and lymphoma cells: Detection with simian antisera. Comparative Leukemia Research, 1975, Bibl. Haemat. No. 43, pp. 24-28, Karger, Basel, 1976.